Many applications, such as those in spacecraft, require a supply of gas at a low pressure. That gas is supplied from a storage container or tank on board the spacecraft in which the gas is confined, compressed to very high pressures. As is known compression allows greater quantities of gas, as measured by weight, to be stored within the available volume of a given storage tank.
One application is in the spacecraft's propulsion system. Most spacecraft depend on propulsion systems to maintain and change their orbits, and to perform attitude control. In virtually all cases compressed gas is used to pressurize and expel propellant from the spacecraft's storage tanks. Ion propulsion systems require a very small gas flow and small system gas volumes are present. Low to moderate pressure gas is also used to pressurize and move liquid hydrazine to monopropellant thrusters forming the craft's propulsion system. The low to moderate pressure gas is obtained from an on-board gas tank, which stores a large quantity of the gas at very high pressure. As an example, gas for operation of a Xenon thruster is stored at 2,175 psia and is dispensed at 37 psi. To drop the gas pressure, pressure regulators are placed in the gas line between the storage tank and the low pressure application. The regulator serves to reduce the gas pressure of the dispensed gas to the low pressure desired and maintain that pressure.
A number of pressure regulator structures, including electro-mechanical types, are known, each having its particular limitations. In the past, several different kinds of pressure regulators obtained from different manufacturers were required to perform the many different active gas regulation functions onboard spacecraft built by the assignee of the present application.
Mechanical pressure regulators typically have their outlet pressure set at the factory. As a consequence other propulsion system components, such as orifices and rocket engines, must be manufactured to a very high accuracy for optimum performance, since the regulator's gas outlet pressure cannot be adjusted, either during development or in-flight. The foregoing regulators do not provide any flexibility after completion of manufacture.
A recently developed pressure regulator of simple structure used on spacecraft, that replaced more complicated regulators, consists of a simple electromagnetically operated gas valve, which either is "on" or "off". By simply opening the valve, gas is permitted to flow through that regulator from the high pressure source into the low pressure sink to replenish spent gas. When the pressure in the sink rises to the desired pressure level, as determined by a pressure sensor or pressure sensors associated with the regulator, the valve re-closes.
To ensure against valve failure in that regulator combination, a common practice is to weld two such valves in gas transmission series relationship, and operate the valves in tandem. Thus should one valve become stuck in the open condition, the remaining serially connected valve, by itself, will shut off the flow of gas. Such redundancy is obviously desirable aboard spacecraft, since a defective valve that is stuck open cannot be replaced during unmanned space flight.
A particular type of control system, one that controls a two position actuator, such as an on/off valve, is classically referred to as a "Bang-Bang" control system. For like reason, the pressure regulator in that system is known in the industry as a "Bang-Bang" regulator. This simple and reliable valve type pressure regulation system has proven cost effective and effective in performance in practice, having been successfully employed on the NASA-BMDO CLEMENTINE spacecraft on its mission to the Moon in the year 1994.
As an advantage, the present invention also employs such simple electromagnetically operated on-off gas valves as a pressure regulator to accomplish pressure regulation and incorporates such a Bang-Bang type pressure regulation mode.
Accordingly, an object of the present invention is to provide a gas pressure regulator of great flexibility, one that permits easy adjustment of the desired outlet gas pressure.
A further object of the invention is to provide a gas pressure regulator whose outlet pressure may be adjusted remotely, either by wireless transmission, data buses or otherwise.
A still further object of the invention is to avoid or minimize the necessity of using multiple gas pressure regulator designs within a given spacecraft or spacecraft product line by providing a gas pressure regulator design that is useful for regulation of pressure in essentially all gas systems found onboard spacecraft.
And an additional object of the invention is to simplify the structure and enhance the flexibility and versatility of gas pressure regulators.